We have action=credit for generating an author list (although permanently disabled on Wikimedia projects, see T49721) but no API equivalent. That should be fixed (especially now that the architecture principles say APIs must provide easy access to authorship information).
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I imagine this would require a (page, actor) index on revision. action=credit is disabled on Wikimedia projects because without such an index WikiPage::getContributors() is too expensive.
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There is a api module to get some information: https://en.wikipedia.org/w/api.php?action=help&modules=query%2Bcontributors
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Per @Umherirrender, this already seems to exist. Feel free to reopen if you have a use case that isn't satisfied by that module.